The invention relates to a magnetic tape cassette and a method of assembling a magnetic tape cassette in which a plate spring having a press pad is disposed in the vicinity of a magnetic head hole which opens on the front face of the body case of the cassette consisting of upper and lower cassette halves, and a magnetic shield plate is disposed behind the plate spring.
Recently, as in the case of digital audio tape recorders and other electronic devices, cassette tape recorders are improving in the areas of miniaturization, lightness in weight, and performance. Correspondingly, audio magnetic tape cassettes need to enhance their performance and undergo various improvements.
FIGS. 6 to 8 show the basic structure of an audio magnetic tape cassette of the prior art. As shown in FIG. 6, in the magnetic tape cassette, a hollow inner space, which is defined by a pair of upper and lower cassette halves 1 and 2 (the upper cassette half is not shown), is divided into a record/reproduction region 4 and a hub housing region 5 by a partition 3.
In the hub housing region 5, hubs 12, rotation guide rollers 13, etc. are disposed so as to be symmetrical about the center line C, which elongates along the longitudinal direction, i.e., front and rear direction, of the cassette. In the record/reproduction region 4, capstan holes 6, cassette positioning holes 7, head pins 8, etc. are formed so as to be symmetrical about the center line C. A plate spring 10, which is a plate-like supporting member and which supports a press pad 9, is disposed behind the head pins 8, and a shield plate 20 is disposed behind the plate spring 10.
As shown in FIG. 8, when a record or reproduction process is to be conducted, a magnetic head 15 of a record/reproduction device is inserted into the record/reproduction region 4 through a magnetic head hole 14 on the front face of the cassette, and the front end of the magnetic head 15 pushes a magnetic tape T together with the press pad 9 into the cassette. As a result, the portion of the magnetic tape T extending between the paired head pins 8 is pressed against a head gap formed at the front end of the magnetic head 15, by the tension of the magnetic tape T and the urging force of the plate spring 10.
As shown in FIG. 7, the shield plate 20 has a U-like shape in the plan view and is positioned and fixed by fitting the upper edge 211 and the lower edge 212 of the shield body 21 into narrow grooves formed on the upper and lower cassette halves 1 and 2. As shown in FIGS. 6 and 8, the magnetic tape T contacts the paired head pins 8. During a recording or reproducing process, the magnetic tape T slides on the head pins 8. Also, the shield plate 20 magnetically shields the area behind the magnetic tape T so that the magnetic head 15 does not pick up noise from this area. The plate spring 10 having the press pad 9 at its center is movably fitted into small gaps formed between the front faces of wings 23 of the shield plate 20 and the paired head pins 8.
When a magnetic tape cassette of the above construction is used, the vibration of a driving system of the record/reproduction device may cause the shield plate 20 to vibrate. The vibration of the shield plate 20 makes the upper and lower edges 211 and 212 rub against and scrape the inner faces of the upper and lower cassette halves 1 and 2. Fine powder produced by the scraping scatters inside the cassette, thereby possibly causing drop-out.
To overcome this problem, various methods of fixing a magnetic shield plate have been proposed. For example, Japanese Utility Model Publication (Kokai) No. HEI2-123775 discloses a cassette wherein deformable receiving portions into which edges of a magnetic shield plate can bite are formed on inner faces of upper and lower cassette halves so as to respectively oppose upper and lower edges of the magnetic shield plate, or spikes protrude from upper and lower portions of a magnetic shield plate so that the spikes pierce inner faces of upper and lower cassette halves.
Japanese Utility Model Publication (Kokai) No. HEI2-65281 discloses a cassette wherein a magnetic shield plate is embedded in narrow ribs formed on inner faces of upper and lower cassette halves.
In the cassettes of the latter two Kokai, the magnetic shield plate is fixed into upper and lower cassette halves. However, when assembling the cassettes, finely crushed powder and scraped powder are unavoidably produced from the portions of the inner faces of the upper and lower cassette halves where the magnetic shield plate bites into the upper and lower cassette halves. Consequently, it is impossible to eliminate the possibility that such powder will adhere to the face of the magnetic tape and cause drop-out.
According to the method of positioning and fixing the shield plate 20 in a cassette assembling process, the plate spring 10 must be inserted into narrow clearances between the shield plate 20 and the head pins 8. For ease of assembly, (the work of dropping the plate spring into the clearances), the clearances must have a substantially large size. This causes a problem in that the plate spring 10 is provided with chattering along the longitudinal direction, and hence the press pad 9 will be unstable as it presses on the tape.
Methods of assembling a plate spring having a pad are disclosed in, for example, Unexamined Japanese Utility Model Publications (Kokai) Nos. Sho. 60-142876, Sho. 60-142877, Sho. 58-43682, and Sho. 58-43686.
In the configurations disclosed in Unexamined Japanese Utility Model Publications (Kokai) Nos. Sho. 60-142876, and Sho. 60-142877, a plate spring is dropped into a narrow clearance formed by ribs having an adequate shape, or an edge of a plate spring is fittingly attached to ribs. However, such configurations in which a narrow clearance is formed by ribs have a problem in that the assembly of the plate spring is difficult, and the strength of a mold for forming a cassette half is liable to be lowered.
In the configurations disclosed in Unexamined Japanese Utility Model Publications (Kokai) Nos. Sho. 58-43682, and Sho. 58-43686, a plate spring is deformed in a process of assembling the plate spring and the engagement of the plate spring is elastically conducted. In such a configuration, the assembly of the plate spring is very difficult. Because of the spring back of the plate spring, moreover, it is very difficult to equally form the lateral side portions on both sides of the pad in a process of forming the plate spring. Eventually, it is difficult to provide a uniform pressing force exerted by the pad, and also to stably enhance the head touch accuracy of a magnetic tape.